In the telecommunication field, operators are able to simultaneously provide broadband ADSL or VDSL telecommunication service as well as narrowband telecommunication services (POTS/ISDN service) via copper twisted pair, e.g. ADSL over POTS (Plain Old Telephone Service), ADSL over ISDN, and VDSL over POTS, and such applications are already quite common. In the present invention, ADSL and VDSL are referred to as xDSL, namely X Digital Subscriber Line.
In order to enable a telecommunication system provide services of such applications, it is required that, corresponding to each copper twisted pair, namely, to each subscriber, a Low Pass Filter (LPF, generally called a separator), a low-frequency (POTS or ISDN) signal service processing circuit, a High Pass Filter (HPF) and a high-frequency signal (xDSL signal) processing circuit be configured at the Central Office (CO) and the Customer Premises Equipment (CPE), respectively, so as to connect the copper twisted pair, i.e. the subscriber.
A typical broadband/narrowband telecommunication system in the prior art is shown in FIG. 1, wherein a subscriber external line 1 of the CPE equipment 1˜n are connected to a Main Distribution Frame (MDF) 15 of CO, the MDF 15 connects the subscriber external line 1 to a broadband access device (DSL Access Multiplexer, DSLAM) 14 of CO via electric cables 3 and 6 as well as to a narrowband exchange device 13 of CO via an electric cable 19.
There is a mixed signal composed of a high-frequency xDSL. signal and a low-frequency POTS/ISDN signal on the subscriber external line 1. At the CO side, the subscriber external line 1 is physically connected to the CO broadband DSLAM 14 through an external line module 17 on a frame 9 of MDF 15, a jumper 20 and an internal line module 2 of MDF and then through the internal electric cable 3.
Inside the broadband DSLAM 14 at CO, there are at least one separator (LPF) card 5, at least one broadband line card 7, a power supply unit and a master control module 16, wherein the broadband line card 7 is an xDSL line card.
The mixed signal on the subscriber external line 1 is output to LPF card 5 and broadband line card 7, wherein each LPF card 5 comprises a number of (n) LPF circuits and each LPF circuit performs as a low-pass filter for filtering the mixed signal of its corresponding subscriber line, and then the separated narrowband signal (POTS/ISDN signal) is transmitted to the narrowband line card in the narrowband device 13 (POTS card or ISDN card) at CO through an internal line module 8, a jumper 21, an internal line module 18 and an electric cable 19 of the MDF 15 for service processing, and each narrowband line card comprises a number of (m) service processing circuits.
Inside each broadband line card 7, there are a number of (p) High Pass Filters (HPF) as well as the same number (p) of xDSL service processing circuits (ATU-C). After each HPF has filtered the low-frequency POTS/ISDN signal of its corresponding subscriber line, the corresponding xDSL service processing circuit (ATU-C) will perform a service processing of the xDSL signal.
The narrowband switching device 13 at CO comprises a narrowband line card as well as a master control and a narrowband service processing module.
The processing at CPEs 1˜n is similar to the processing at CO, wherein CPE separator (LPF) separates the narrowband signal from the mixed signal of subscriber external line 1 and sends the narrowband signal to the subscriber's phone set, and meanwhile the mixed signal is transmitted to a Remote Telephone Unit (RTU), the High Pass Filter (HPF) configured inside the RTU filters the low-frequency POTS/ISDN signal from the mixed signal and then performs a service processing of the high-frequency signal (xDSL signal).
In practical applications, the number of ports comprised in each external line module of the distribution frame is usually equal to the number of ports comprised in each internal line module of the distribution frame; a typical case comprises 128 ports or 100 ports. (Note: the so called external/internal line module of distribution frame is the connector bank of twisted pair, and two connectors corresponding to a twisted pair is called one port).
Each LPF card comprises a number of circuits for connecting a number of subscriber lines, for example, 32 circuits can connect 32 subscriber lines. Likewise, each narrowband line card also comprises a number of circuits, say 32 or 16 circuits; so does each broadband line card, say 32 or 48. A LPF card, a broadband line card and a narrowband line card do not necessarily comprise the same number of circuits, respectively. A LPF card and a broadband line card are usually configured as comprising the same number of circuits respectively.
In FIG. 1, there is a line test module 22 configured at CO for use in testing subscriber line malfunction.
In practical applications, since the subscriber external line 1 between CPE and CO MDF is located outdoors, it is prone to have a malfunction due to touching other lines, getting disconnected, touching a power line, getting immerged or other external reasons. Therefore, a proper testing device is set at CO for measuring parameters of the subscriber line, such as line voltage, line resistance, line capacitance, line background noise, and line balance degree to ground, so as to detect and identify malfunctions and make malfunction reports. Based on the malfunction reports, a telecommunication operator can arrange its personnel to repair the line malfunctions.
The line test module 22 is usually located in a device or system outside DSLAM, or located in a module inside DSLAM.
In order to enable line test module 22 to test every subscriber line connected to DSLAM, it is required to configure at each subscriber interface circuit a switching device for switching connecting directions of a subscriber line, which is usually referred to as a “line capturing test relay” or switching test relay. The function of a line capturing test relay, i.e. “line capturing test”, is to switch a subscriber line connected to the DSLAM subscriber interface circuit to the automatic test device for line malfunction.
In order to implement the “line capturing test”, it is needed to set a “line capturing test relay” in each subscriber interface circuit of each LPF card, of which the operating principle is shown in FIG. 2. FIG. 2 is a schematic diagram illustrating the operating principle of a line capturing test relay in FIG. 1, wherein each subscriber line must pass a line capturing relay 12 before entering the LPF circuit 11 and the broadband line card 7.
It can be seen from FIG. 2 that, when the line testing device is not testing subscriber lines, a subscriber external line is directly connected to the service processing circuit at CO (LPF 11, HPF on broadband line card 7 and ATU-C 10) through the closing contact of line capturing relay 12 (shown by the solid line in FIG. 2), namely the subscriber line and CO circuit are connected as normal. When the automatic test device is testing the first subscriber external line, the connecting direction of this subscriber external line will be switched through line capturing relay 12 and then this subscriber external line will be connected to the line testing device 22 via a test bus 23, while subscriber external lines of other subscribers and CO circuits are still normally connected.
In practical applications, LPF circuit 11 is composed of capacitors, inductors and other passive electronic devices. If there are no other active electronic circuits or devices in the internal circuit of a LPF card, this LPF card can be a passive circuit board. However, in the technical scheme of the prior art as shown in FIG. 2, since a line capturing test relay of the subscriber line is set inside an LPF card and the relay cannot operate without power supply, the LPF card needs to introduce power supply from the system back board in the cabinet of the DSLAM so as to supply power to the line capturing relay. Therefore, an LPF card in such a case is an active circuit component and cannot normally operate when disengaged from the system back board in the DSLAM cabinet, namely the LPF card cannot be separated from the DSLAM cabinet which has a power supply component configured in it; in addition, an active LPF card circuit board is more complicated than a passive one.
As the line capturing relay set in the LPF card of the broadband DSLAM at CO increases the complexity of LPF card, a second type of broadband/narrowband telecommunication system has emerged. As shown in FIG. 3, which is a schematic diagram illustrating the second type of broadband/narrowband telecommunication system in prior art, a test device is set between the original MDF 15 and the DSLAM 14 at CO. The test device is composed of a line capturing matrix module 24 and a test module 25, wherein the line capturing matrix module 24 captures a designated subscriber line for the test module 25, and the test module 25 tests the parameters of this line, such as electric resistance, capacitance, voltage, background noise, longitudinal degree of balance and etc. The test module 25 can also be implemented by an external test device.
In this broadband/narrowband telecommunication system, all line capturing relays are separated from the LPF card and set inside one line capturing matrix module 24 so that a large number of commercial “LPF cards without line capturing relays” already employed in this field can be used continuously.
The test device of the broadband/narrowband telecommunication system as shown in FIG. 3 is rather complicated as it has to perform such functions as power collecting, communications with DSLAM, line capturing/line release, and line testing. If an external test device is adopted to implement the functions of a test module, the line capturing matrix device and the test device have to get power supply and communicate with DSLAM, respectively, which further increases the complexity of the entire system.
Besides, since an entrance port and an exit port must be set inside the test device for the wiring of each subscriber line, the test device has to comprise a large number of ports, leading to the massive size and high price of the test device as well as a pretty high average cost for each subscriber.